ASTM A312 TP317L Stainless Steel Welded Pipe: Composition and Applications

What Is ASTM A312 TP317L Welded Pipe?

ASTM A312 TP317L is a low-carbon molybdenum-bearing austenitic stainless steel pipe grade defined in ASTM A312, the standard specification for seamless, welded and heavily cold worked austenitic stainless steel pipes. Designated UNS S31703, TP317L contains 18.00-20.00% chromium, 11.00-15.00% nickel and 3.00-4.00% molybdenum, with carbon limited to 0.035% maximum. The combination of molybdenum at 3-4% and the very low carbon content gives TP317L markedly better resistance to pitting, crevice corrosion and attack by many reducing acids than the 316L family, while keeping full weldability without post-weld heat treatment.

Chemical Composition (ASTM A312 TP317L)

Composition limits per ASTM A312 for grade TP317L (UNS S31703), in weight percent:

Element	Limit (%)
Carbon (C)	0.035 max
Manganese (Mn)	2.00 max
Phosphorus (P)	0.045 max
Sulfur (S)	0.030 max
Silicon (Si)	1.00 max
Chromium (Cr)	18.00-20.00
Nickel (Ni)	11.00-15.00
Molybdenum (Mo)	3.00-4.00
Nitrogen (N)	0.10 max

Mechanical Properties (Room Temperature)

Minimum mechanical properties required by ASTM A312 for TP317L in the solution-annealed condition:

Property	Value
Tensile Strength	515 MPa min
Yield Strength (0.2% offset)	205 MPa min
Elongation	35% min

The pitting resistance equivalent number (PREN = Cr + 3.3 Mo + 16 N) of TP317L is approximately 30, which is well above the value of about 25 for 316L and explains its superior behavior in chloride-bearing media.

Corrosion Resistance

TP317L resists pitting and crevice corrosion in chloride environments far better than 316L, and it performs well in sulfuric and phosphoric acids at moderate concentrations and temperatures. It is widely used in chlorine dioxide bleaching stages in pulp mills, in flue gas desulfurization (FGD) absorber internals, and in dye, agrochemical and pharmaceutical plants handling aggressive process streams. In strongly reducing acids such as hot concentrated hydrochloric acid, no austenitic grade is adequate, and higher-alloy or nickel-base alloys must be considered.

Manufacturing and Dimensional Range

TP317L welded pipe is manufactured by TIG welding (autogenous or with matching filler) or by ERW, followed by full solution annealing and pickling or bright finishing. The welded product is produced in outside diameters from about 15 mm to 800 mm with wall thicknesses from 1.0 mm to 12.0 mm; larger diameters and special wall schedules can be produced by forming and welding plate. Longitudinal weld seams are normally 100% tested, and the finished pipe is verified against the dimensional tolerances of ASTM A999 or the applicable procurement specification.

Typical Applications

Chemical process piping for sulfuric, phosphoric and organic acid service.

Chlorine dioxide bleaching lines in pulp and paper mills.

Flue gas desulfurization absorber internals and ductwork.

Pharmaceutical and fine chemical equipment requiring clean, weldable low-carbon pipe.

Frequently Asked Questions

What is the difference between TP317 and TP317L? TP317 has a maximum carbon content of 0.08%, while TP317L limits carbon to 0.035% maximum. The low-carbon version avoids sensitization during welding, so TP317L can be used in the as-welded condition without post-weld heat treatment.

What is the maximum service temperature of TP317L pipe? TP317L is mainly a corrosion-grade material; oxidation resistance in air is adequate to about 900 degrees C, but design temperatures above roughly 550 degrees C must be checked against creep-limited allowable stresses, and the low-carbon chemistry is selected for corrosion service rather than for very high temperature strength.

Is TP317L magnetic? No. TP317L is fully austenitic and essentially non-magnetic in the annealed condition; light magnetism may appear after heavy cold forming.

How is TP317L welded pipe manufactured? Strip or plate is roll-formed into a cylinder and joined by TIG or ERW welding, then the pipe is solution annealed and pickled or bright finished. The weld seam is inspected and tested to the requirements of ASTM A312.

Does TP317L require post-weld heat treatment? No. The 0.035% maximum carbon content keeps the heat-affected zone free of significant chromium carbide precipitation, so field welds are normally accepted in the as-welded condition.

What is TP317L equivalent to in other standards? TP317L (UNS S31703) corresponds to EN 1.4438 (X2CrNiMo18-15-4) and is covered as plate and sheet in ASTM A240; the JIS designations SUS317L per JIS G4304/G4305 cover the same stabilized low-carbon family.